Proper functioning of the human shoulder is in part governed by the rotator cuff muscles. These muscles originate from scapula (one of the three shoulder bones) and attach to the humerus via fibrous tendons as they approach the outer aspect of the shoulder thereby surrounding the anterior, superior and posterior of the shoulder joint. The motion of the shoulder is facilitated by the contraction of rotator cuff muscles which pull the rotator cuff tendons. Thus the rotator cuff allows movement of the upper arm for activities such as reaching and throwing.
Disorders of the rotator cuff, particularly tears of the rotator cuff tendons, can cause significant shoulder pain and disability. Young athletes, middle-aged workers, and a substantial portion of the elderly population can suffer a rotator cuff injury which prevents them from working, playing sports, enjoying hobbies or performing routine daily activities. Active people, including athletes, are highly susceptible to rotator cuff problems, particularly as they get older. It has been estimated that more than 100,000 rotator cuff surgeries are performed in the United States each year. Rotator cuff lesions are one of the most common causes of upper extremity disability.
A serious concern with a rotator cuff tear is that the rotator cuff has limited healing potential after tears. The non-surgical treatment for rotator cuff tears includes some combination of anti-inflammatory medication, limiting overhead activity, steroid injections, and strengthening exercises often in association with physical therapy. Surgery to repair the rotator cuff is often advised when a rotator-cuff tear causes severe shoulder weakness or when there has been no improvement following non-surgical treatment. Repair of a torn rotator cuff generally consists of reapproximating the tendon edge to a bony trough through the cortical surface of the greater tuberosity.
Traditionally, surgeons use suture and suture anchors to repair weak, frayed and damaged tissue. Several surgical procedures have been performed to cover massive irreparable rotator cuff tears, including tendon transfer, tendon mobilization and tendon autografts patch grafts using biological or synthetic materials [Aoki et al., 1996 J Bone Joint Surg Br. 1996 September; 78(5):761-6; Gerber 1992 Clin Orthop Relat Res. 1992 February; (275):152-60; Kimura et al., 2003 J Bone Joint Surg Br. 2003 March; 85(2):282-7]. Suture anchors were found to be useful in rotator cuff repair because they could be placed with less surgical dissection and allowed for the “mini-open” technique to become popularized. There are two major disadvantages to using bioresorbable suture anchors that are currently available and used in arthroscopic rotator cuff repair. Passing the suture through the rotator cuff can often be challenging due to the limited amount of working area in the subacromial space. While knots can be tied arthroscopically in a secure fashion, the process is very time-consuming and clearly has a long learning curve. Arthroscopic repair has been suggested for rotator cuff repair, however is burdened by a percentage of recurrences that is greater than the repair carried out when an open technique is used [Bungaro et al., 2005 Chir Organi Mov. 2005 April-June; 90(2):113-9]. It has been found that when an open technique is used, good hold can be guaranteed by using reinforced stitches such as the modified Mason-Allen suture.
The clinical results of all current rotator cuff repair techniques are often sub-optimal and often pre-injury functional levels are not obtained. Augmentation devices have not provided a satisfactory alternative. Several factors limit the extensive use of biological grafts including donor site morbidity, limited availability of autografts material the risk of disease transmission from allografts and patch grafts become mechanically weaker over time as they cause adverse reactions. Extracellular matrices are widely employed by sports-medicine and orthopedic surgeons for augmenting the torn rotator cuff and are intended to strengthen the tendon and enhance biological healing. More recently, synthetic bioabsorbable meshes have been commercialized for repair of soft tissues, including the rotator cuff.
Several extracellular matrix products (ECMs) are commercially available and include GraftJacket (Wright Medical Technology), CuffPatch (Organogenesis, licensed to Arthrotek), Restore (Depuy), Zimmer Collagen Repair (Permacol) patch (licensed by Tissue Science Laboratories), TissueMend (TEI Biosciences, licensed to Stryker), OrthoADAPT (Pegasus Biologics), and BioBlanket (Kensey Nash). These products are fabricated from human, cow, or pig skin, equine pericardium, human fascia latta, or porcine small intestine submuccosa. The manufacturers use various methods of decellularization, cross-linking, and sterilization; the end products possess varying properties of strength, stiffness, and suture-failure load. While there are many products available and many thousands of rotator cuff repairs being performed annually with extracellular matrices, little is known about clinical outcomes. One published study by Iannofti et al found that porcine small intestine mucosa (DePuy's Restore patch) did not improve the rate of tendon-healing or the clinical outcome scores of patients with massive and chronic rotator cuff tears. The relatively low resistance to suture pull-out and potential for immunological response (perceived or real) of ECMs has limited widespread use of ECMs for rotator cuff repair.
Depuy Orthopedics Inc, Warsaw, Ind. has developed SIS (intenstinal submucosa) for augmentation of rotator cuff tendon tears. The SIS materials have sold well, but have the disadvantage of originating from a contaminated animal source, necessitating a variety of cleaning steps. Some patients have sustained swelling, and what appears to be a graft versus host reaction to the SIS Material. GraftJacket is a product by Wright medical using cross banked human cadaver skin. While response levels are lower with this product, the material is very poorly degradable.
Some of the recent studies have indicated some advantages of using synthetic augmentation devices to support the healing of torn rotator cuff. Two synthetic, bioabsorbable products were recently 510 k cleared by the FDA, and both indications for use statements include rotator cuff repair. One of these products is SportMesh (marketed by Biomet) which is made from woven Artelon fibers. Artelon is a biodegradable poly(urethaneurea) material. SportMesh is currently under evaluation for treatment of rotator cuff tears at one or more US-based centers. A second synthetic product recently cleared by the FDA is the X-Repair (marketed by Synthasome) which is made from woven bioabsorbable poly(L-lactic acid) (PLLA) fibers. The X-Repair product was evaluated in a canine model and found to improve biomechanical function at 12 weeks. Another product of interest that was cleared by the FDA is Serica's SeriScaffold, a long-term bioabsorbable woven mesh of silk fibers. Two PLLA devices have been evaluated for rotator cuff repair; one study in sheep reported in 2000 showed a 25% increase in strength of the repair and a second study in goats reported in 2006 showed no significant difference in load to failure of the repair. One study by Koh et al. demonstrated the better biomechanical performance of damaged rotator cuff tendon while healing when the tear was augmented with woven polylactic acid structures [Koh et al., 2002 Am J Sports Med. 2002 May-June; 30(3):410-3]. See, for example, U.S. published application 2008/0051888.
There is a need for an alternative strategy to develop an augmentation device for rotator cuff repair and regeneration due to several reasons. First it has recently been found that up to 60 percent of rotator cuff tendon repairs are failing after repair, even in the hands of good surgeons. While some patients do well after surgery even with the re-torn rotator cuff tear, many do not, and in fact a re-torn rotator cuff is a negative predictor of outcome for a patient. Second, is the fact that traditional outcomes of rotator cuff repair are limited by biology. It takes four weeks to heal a rotator cuff repair, during which patients are not allowed to have significant mobilization of the shoulder. However, the decreased mobility of the joint can lead to significant shoulder stiffness which is a serious disadvantage. This clearly shows the importance of an augmentation device that would allow shoulder mobility while healing. Third, often there are gap areas that cannot be closed with rotator cuff tears. An augmentation device when employed could satisfactorily address this concern.
It is an object of the present invention to provide a biocompatible device for augmentation and repair of rotator cuff injuries.
It is still another object of the present invention to provide a method for producing a device for repair or augmentation of rotator cuff injury which results in improved strength retention and ingrowth of new tissue.